The invention relates to a vacuum filter for the separation of solids from liquids, with a circulating, endless array of troughs which constitute a horizontal filter surface on which an endless filter cloth is laid, in which each trough has an elastic sealing strip on that rimless edge which extends along the trough bottom transversely to the direction of its movement.
Vacuum filters of this kind are already known, in which the conveyor revolves about longitudinally spaced wheels, wherein the upper strand of the conveyor includes a horizontal filter surface provided by a series of troughs which are preferably guided over a stationary vacuum drain. These vacuum filters are used for filtration because in this manner cake formation is promoted by gravity and the washing of the cake can be carried out more effectively.
Thus, the filtering surface of the known vacuum filter is constituted by the upper strand of the endlessly circulating array of troughs or trays which, in their direction of movement, are located directly behind each other, wherein each trough, in the direction of movement, is connected with the next adjacent trough by a sealing strip. Owing to the rimless construction of each trough, the aforementioned filter cloth can be laid over the filtration zone, that is to say, upon the filtering surface. Between the front edge of the rearward trough as viewed in the direction of movement and the rear edge of the front trough in the direction of movement a sealing strip must be located, in order to seal off the vacuum from the atmosphere. The reason for this is that each trough has its own connection with the vacuum drain located underneath and is so constructed, that the trough and the vacuum drain together form a sliding seal. The vacuum effects the drawing off of the liquid from the material residing on the filter cloth and, therefore, the seal constituted by the aforementioned sealing strip at the joint between two successive troughs must be as tight as possible.
Numerous concepts have already been advanced with regard to the known vacuum filters concerning the manner in which satisfactory cleaning and servicing including repairs can be carried out whilst maintaining proper functioning of the machine, that is to say, while separating solids from liquids. It is necessary to provide readily replaceable parts at locations in the vacuum filter apparatus subject to wear.
One part particularly subject to wear is the sealing strip located between the troughs adjacent each other in the direction of movement. The known vacuum tray-belt filters have a great number of such troughs and, for constructional reasons, between each trough there is a gap which must be flexibly sealed in order to prevent a loss of vacuum. Although the known vacuum filters have sealing strips between the troughs, it has been found that these sealing strips sometimes fail to ensure the tightness required for the vacuum applied to the filter surface and, in particular, are subjected to destructive abrasion after only a relatively short period of operation, so that the sealing function is impaired and the sealing strip has to be replaced. The replacement of these sealing strips, called tray seals, has proved difficult in conventional machines, being especially time-consuming, with the result that undesirably long downtimes of the vacuum tray-belt filters occurs.
The task to which the invention is directed is therefore one of improving a vacuum filter of the type described above so as to achieve a good vacuum seal, especially between successive troughs, and with easier replaceability of the sealing strips.